The Automatic Option

Manumatic transmission was a great idea. As the name implies, it is a half-way house between a manual and a fully automatic gearbox, doing away with the clutch pedal but retaining the gear lever. To quote the description in the manual ‘With the aid of the Manumatic Transmission System, a perfect gear change requires no other action than the appropriate movement of the gear lever’. In principle the system was very simple. An electric switch mounted on the gear lever was operated when the knob was held and caused the clutch to disengage. When the change had been completed, the lever would be released and the clutch would be re-engaged. But while the theory is straightforward, putting it into practice complicates the issue a bit. The trouble is that, when you change gear, it’s not just a question of banging the clutch in and out like a switch. Though, coming to think about it, there are some (Egyptian taxi drivers spring to mind as one example), who may not agree. But for the rest of us, some attempt has to be made to co-ordinate throttle and clutch to achieve a nice, smooth change, and this is the part that taxed the engineers in the 1950s. Fig. SA. 1 gives an idea of the apparatus that was required to do this. It is reproduced from the workshop manual, which takes four pages to describe how everything works and a further 33 on how to mend the system when it goes wrong. The editorial blue pencil would undoubtedly be wielded with a vengeance if I went into detail, so I will try to be brief... For a start, the clutch is of the centrifugal type, so that when the engine is idling it is disengaged, but then steadily engages as the engine revs rise. This means that, to start from rest, you grasp the ever, which disengages the clutch, pop it into first and release the lever again. The car will not move until you pass down the accelerator pedal, which causes the centrifugal clutch to engage. and off you go. When you get bored with first gear, you grasp the lever again to select another one. And here is the clever bit. This can be done with the accelerator pedal in any position - the system incorporates two vacuum operated throttle servos which control the opening and closing of the throttle independently of the pedal’s position. One of these is controlled by the clutch servo and closes the throttle when the gear change commences.The other is controlled by a solenoid operated valve in circuit with a synchronising switch on the clutch cover. If the engine speed falls below the driven plate speed, the throttle opening servo kicks in to increase the engine speed and ensure that nice, smooth take-up which all except those Egyptian taxi drivers aspire to. And to make absolutely certain, a pedal valve is incorporated in the control unit which ensures a progressive engagement of the clutch. Fig. SA.2 Shows how all these bits and pieces fit together and indicates what is happening when the car is at rest and in gear. The last picture clearly shows the black control box mounted behind the engine on top of the bell housing, together with the linkages from the two servos to the throttle. In nearly 20 years of attending Magnette events I have never seen a Manumatic car, and the Register has details of only three or four that are know to exist, none being road worthy. Records show that a total of only 494 were produced, most of which were exported to North America. So why was such a clever system such a flop? A clue is given by Peter Woods’ own car, which he bought for a snog from a main dealer in Oxford because the transmission was faulty. The cure was simple - two of the wires in the control unit had been swapped over by a puzzled fitter and when they were swapped back, all was well.. The basic trouble with the system was its complexity; it incorporated a large number of components of unique design, which had an almost infinite capacity for failing. This seems to have been combined with an inability of BMC dealers to diagnose the faults properly when they occurred. So it is hardly surprising that the system rapidly got a dreadful reputation, second-hand values plummeted and many of the original cars were converted back to standard form by frustrated owners. Written by Paul Batho

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